I haven’t run into any mention. I don’t know why they wouldn’t do them all, eventually. Unfortunately, we can only guess when. As for why not yet, I’d guess maybe they do a production run of gen2s based on demand of that keyboard, and perhaps how large the stock of originals is. And since Japan isn’t yet a supported region for sales, I’d imagine demand is low. All purely guesses, though.
I would suggest asking support, if you haven’t already. There is always a chance that it was supposed to be listed already.
The 2nd gen keyboards seem to have come out February